The present invention relates to a technique concerning a high temperature component used under a high temperature corrosive or oxidative atmosphere in a gas turbine, a jet engine or the like. In particular, the present invention relates to a high temperature component and a gas turbine high temperature component which can improve a thermal barrier performance by subjecting a surface of a metal base material to a thermal barrier coating (TBC) and also relates to a method of manufacturing the same.
In order to improve a heat efficiency, research and development for high temperature (a rise of working gas temperature) have been earnestly made in a prime mover such as a gas turbine, a jet engine or the like. In view of materials for high temperature, there is a tendency for a component material to be exposed to a sever working environment such as high temperature. Therefore, in gas turbine components, in particular, in a movable blade, a stationary blade and components directly exposed to a combustion gas of a combustor, the following two matters have been studied so that these components can provide an durability under a high temperature improve a cooling characteristic and to improve a heat resistant temperature of materials.
First, the following is a description on a study for improving the cooling characteristic in order to reduce a temperature of component materials.
In order to improve the cooling characteristic, it is effective to use a gas having a high heat capacity or to increase a cooling gas flow rate in principle. However, according to the method of using a high heat capacity gas or the method of increasing a cooling gas flow rate, a combustion gas temperature is reduced, and conversely, there are many cases where a heat efficiency lowers. In view of such circumstances, the following methods are employed as a method of improving a cooling performance without lowering a combustion gas temperature. More specifically, there are provided a method of increasing a heat conductivity between a material and a cooling gas and a method of increasing a contact area of the material and the cooling gas.
Film cooling or impinge cooling will be listed up as a a typical example of the method of increasing a heat conductivity between a material and a cooling gas. Moreover, a return flow structure of a blade cooling passage is mentioned as a typical example of the method of increasing a contact area of the material and the cooling gas. As described above, a heat is effectively eliminated as occasion demands. However, in any case of using these methods, a structure of equipments is made into a large size, and the component structure becomes complicated. For this reason, a manufacturing cost of equipments is increased and the system becomes complicated.
Next, the following is a description on a study for improving a heat resistant temperature of the material.
Conventionally, as a heat resisting structural material, a unidirectionally solidified or monocrystalized superalloy has been developed. The superalloy uses any one of Ni-base, Co-base or Fe-base material as a main component. On the other hand, there has been developed an intermetallic compound which is excellent in oxidation resistance by adding Nb- and Mo-base element or the like, and thereby, a trial of further improving a strength to a high temperature is made. However, in the unidirectionally solidified or monocrystalized superalloy, a usable critical temperature is 1000xc2x0 C. at most in view of a melting point of the superalloy. Moreover, in the case of the superalloy to which Nb- and Mo-base element are added in order to improve an oxidation resistance, there is a problem that a workability is made worse and the manufacturing cost thereof becomes high.
Moreover, there has been developed a method of improving a heat resistance of a high temperature component by applying a ceramic material, which has a high melting point and is excellent in an oxidation resistance and in a corrosion resistance, to the high temperature component. In fact, a SiC- and Si3N4-base ceramic is applied as the high temperature component. However, the ceramic has a weak toughness in comparison with a metallic material, and there is therefore provided a problem that a workability is made worse, and an involved cost becomes high. For this reason, many problems have caused in order to realize a high temperature resisting strength and cost decreasing to widely use the ceramic as a structural material of the high temperature component.
On the other hand, there is a method of using a metallic material having an excellent toughness as a base material of the high temperature component, and subjecting a surface of the metal base material to the thermal barrier coating (TBC), and thus, improving a heat resistance of the high temperature component. The thermal barrier coating is an oxide-base ceramic layer having a low heat conductivity, and a heat is cut off by forming the thermal barrier coating on the surface of the metal base material so as to prevent a rise of the temperature of a metal base material.
For example, as disclosed in Japanese Patent Laid-open Publication No. SHO-62-211387, there has been proposed a method of forming a thermal barrier ceramic layer having a thickness of a few hundred xcexcm on the surface of a metal base material so that a rise of the temperature on the surface of the metal base material can be reduced by several tens of degree (xc2x0 C.). According to this method, it is possible to restrain the rise of the temperature on the surface of the metal base material. Therefore, a gas turbine can be made high temperature, and that is, in the thermal barrier coating, the thicker the thickness of the thermal barrier ceramic layer is, the more a thermal barrier performance is excellent, and thereby, it is possible to reduce a temperature of the metal base material. Further, by subjecting the surface of the metal base material to thermal barrier coating, a heat flux from a combustion gas side to a cooling air side becomes small. Thus, a cooling gas flow rate can be reduced.
However, in the thermal barrier ceramic layer, to which the aforesaid coating is subjected, a crack and peeling from the base material constitute the great problem. For this reason, various research and development have been made in the prior art in order to solve the problem of the peeling.
A two-layer structure is representative of the thermal barrier coating for solving the problem of peeling. The two-layer structure is formed by coating the following two layers, that is, a MCrAlY alloy layer (M is Fe, Co or Ni) coated on the surface of the metal base material, and an oxide-base ceramic layer having a low heat conductivity coated on a surface of the MCrAlY alloy layer. In this case, a zirconia-base ceramic is used as the oxide-base ceramic layer.
The thermal barrier coating having the two-layer structure is usually formed by a thermal spray process. However, in the case where coating is carried out in an atmospheric air, the thermal barrier coating layer becomes porous, and for this reason, there is a problem that an adhesive strength to the metal base material lowers, or corrosion resistance and oxidation resistance are deteriorated. In order to solve such problems, in recent years, there has been developed a method of carrying out a plasma spraying in a low pressure inert gas atmosphere substantially excluding an air (which is generally called as a low pressure plasma spraying) and thereby, a durability of the thermal barrier coating has been greatly improved.
Various studies about a material for forming the thermal barrier ceramic layer have been made.
More specifically, in zirconia (ZrO2), a phase transformation takes place in the vicinity of 1200xc2x0 C.; for this reason, an improvement in a phase stabilization and heat cycle characteristic is achieved by adding an additive for stabilizing the zirconia.
Moreover, in the case of forming the thermal barrier ceramic layer, a thermal barrier coating layer having a columnar structure is formed with the use of an electron beam physical vapor deposition (EB-PVD), and thereby, the structure is improved so as to make long a lifetime of the gas turbine.
However, in the aforesaid thermal barrier coating, it is a matter of general that a zirconia-base ceramic having a low heat conductivity is used, and a thermal barrier performance has not been controlled. For this reason, it is impossible to obtain thermal barrier coating having an excellent thermal barrier performance.
Moreover, for example, in a gas turbine movable blade, a gas turbine stationary blade and a combustor, which are exposed to a high temperature combustion gas, it is a matter of course that a temperature load condition is different depending upon portions of the blade to be exposed. However, almost no control is carried out so as to obtain a proper thermal barrier performance in accordance with the temperature load condition, and a thickness of a thermal barrier ceramic layer is merely varied. Thus, the thermal barrier ceramic layer has the same thickness everywhere in the portions thereof, and for this reason, the thermal barrier characteristics in these portions are the same, and the surface temperature of the metal base material which is a strengthening member tends to be considerably different at the portions thereof.
As described above, the thermal barrier characteristic mentioned above is not taken into consideration, and accordingly, there are the following problems. More specifically, many cooling medium are required, and further, a temperature gradient in a thickness direction is relatively great, and for this reason, there exists a hot spot having local high temperature portion due to a gas holder (spot) such as a combustion gas and a cooling gas. Therefore, it is necessary to improve a lifetime of the metal base material, a heat efficiency of a gas turbine and reliability.
An object of the present invention is to eliminate the problems or defects mentioned above and to provide a high temperature component and a manufacturing method thereof capable of controlling a thermal barrier performance of a thermal barrier coating in accordance with an environment to which the component is exposed and making uniform a surface temperature of a base material so as to improve a thermal barrier characteristic.
Another object of the present invention is to provide a gas turbine high temperature component and a manufacturing method thereof capable of making uniform a surface temperature of a metal base material in the thermal barrier coating of a gas turbine used in a combustion gas atmosphere and improving a heat efficiency, lifetime and reliability in the gas turbine.
These and other objects can be achieved according to the present invention by providing, in one aspect, a high temperature component comprising:
a base material; and
a thermal barrier coating coated on a surface of the base material,
wherein the thermal barrier coating has a thermal barrier characteristic controlled in accordance with an environment to which a high temperature component is exposed so as to make substantially uniform a surface temperature of the base material.
In a preferred embodiment in this aspect, the surface temperature of the base material has a difference in temperature within 100xc2x0 C. between portions thereof.
The thermal barrier coating comprises a thermal barrier ceramic layer and a thermal barrier characteristic of the thermal barrier ceramic layer is controlled by varying a thickness or porosity thereof at portions of the thermal barrier ceramic layer.
In another aspect of the present invention, there is provided a gas turbine high temperature component comprising:
a metal base material made of a heat resistant alloy essentially consisting of at least one of Ni-base, Co-base or Fe-base; and.
a thermal barrier coating coated on a surface of the metal base material,
wherein the thermal barrier coating has a thermal barrier characteristic controlled in accordance with an environment to which a high temperature component is exposed so as to make substantially uniform a surface temperature of the base material.
In a preferred embodiment in this aspect, the gas turbine high temperature component is at least one of a movable blade and a stationary blade.
The thermal barrier coating comprises a thermal barrier ceramic layer and at least one thermal barrier ceramic layer formed to a leading edge surroundings or a trailing edge surroundings of the movable blade or the stationary blade having a relatively high temperature has a thickness larger than that of another portion of the blade. The thermal barrier ceramic layer has a thickness ranging from 0.1 mm or more to 1.0 mm or less on a thicker side thereof and a thickness ranging from 0 mm or more to 0.5 mm or less on a thinner side thereof and the thickness of the thinner side thermal barrier ceramic layer is thinner than the thicker side thermal barrier ceramic layer.
The thermal barrier coating comprises a thermal barrier ceramic layer and the thermal barrier ceramic layer formed on a back side of the movable blade or the stationary blade having a relatively high temperature has a thickness larger than that of the thermal barrier ceramic layer formed on a belly side thereof having a relatively low temperature. The thermal barrier ceramic layer has a thickness ranging from 0.1 mm or more to 1.0 mm or less on a thicker side thereof and a thickness ranging from 0 mm or more to 0.5 mm or less on a thinner side thereof and the thickness of the thinner side thermal barrier ceramic layer is thinner than the thicker side thermal barrier ceramic layer.
The thermal barrier coating comprises a thermal barrier ceramic layer and at least one thermal barrier ceramic layer formed to a leading edge surroundings or a trailing edge surroundings of the movable blade or the stationary blade having a relatively high temperature has a porosity larger than that of another portion of the blade.
A surface temperature of the metal base material is made uniform by making higher a porosity of a back side of the movable or stationary blade having a relatively high temperature than that of a belly side thereof. The porosity of the thermal barrier ceramic layer ranges from 10% or more to 40% or less on a higher side thereof and ranges from 2% or more to 20% or less on a lower side thereof.
An oxide-base ceramic is used as a material of the thermal barrier ceramic layer and the oxide-base ceramic essentially comprises ZrO2 and at least one or more of additives MgO, CaO, Y2O3 or CeO2. An oxide-base ceramic is used as a material of the thermal barrier ceramic layer and the oxide-base ceramic essentially comprises at least one of Al2O3, HfO2, ThO2 or BeO.
The surface temperature of the base material has a difference in temperature within 100xc2x0 C. between portions thereof. The thermal barrier coating comprises a thermal barrier ceramic layer and a thermal barrier characteristic of the thermal barrier ceramic layer is controlled by varying a thickness or porosity thereof at portions thereof.
In a further aspect of the present invention, there is provided a method of manufacturing a high temperature component comprising the steps of:
preparing a base material; and
applying a thermal barrier coating comprising a thermal barrier ceramic layer on a surface of the base material by varying at least one of thickness or porosity of the thermal barrier ceramic layer at portions thereof.
In a still further aspect of the present invention, there is provided a method of manufacturing a gas turbine high temperature component comprising the steps of:
preparing a metal base material made of a heat resistant alloy essentially comprising at least one of Ni-base, Co-base or Fe-base; and
applying a thermal barrier coating comprising a thermal barrier ceramic layer on a surface of the metal base material by varying at least one of thickness or porosity of the thermal barrier ceramic layer at portions thereof.
In a preferred embodiment in this aspect, the thermal barrier ceramic layer is formed by spraying a raw powder of a thermal barrier ceramic material at a high speed by means of heating source such as plasma.
A supply amount of raw powder, a grain size of the raw powder, a feed rate of a thermal spraying gun, an angle of the thermal spraying gun, a spray distance and a spray power are optimized and a deposition rate which is a coating thickness formed per one pass is varied so as to vary a thickness or porosity of the thermal barrier ceramic layer depending upon portions to be sprayed.
In a case of forming a thermal barrier ceramic layer on a metal base material, a target material is heated and vaporized by means of an electron beam and the vapor thus obtained is deposited on the surface of the metal base material so as to form the thermal barrier ceramic layer. The raw powder of the thermal barrier ceramic is passed through a plate having a different space ratio so as to vary the deposition rate.
According to the present invention of the characters mentioned above, in one aspect, it is possible to make uniform the surface temperature of the base material by varying a thermal barrier characteristic of the thermal barrier coating depending upon portions of the high temperature component. Thus, the surface temperature difference of the base material between the portions is made little, so that a lifetime of the base material can be improved, and also, a reliability of the high temperature component can be secured. Moreover, the high temperature component is applicable to an outer wall of a jet engine or a rocket which is exposed to a high temperature environment.
Furthermore, in this aspect, the surface temperature difference between the portions of the base material is set within 100xc2x0 C. The surface temperature difference is within the temperature range, and thereby, it is possible to improve a lifetime of the base material.
According to the present invention, it is possible to improve the thermal barrier characteristic of the thermal barrier coating by making larger a thickness of the thermal barrier ceramic layer or by making higher a porosity thereof.
In another aspect, in the metal base material, various development have been made in the prior art in order to secure a strength. There has been variously developed a unidirectionally solidified and monocrystalized (single crystal) superalloy which essentially comprises one of Ni-base, Co-base or Fe-base. In order to secure a thermal barrier performance, a thermal barrier coating layer is formed on the metal base material, and thus, it is possible to obtain a high temperature component which has an excellent strength even in a high temperature environment.
In this aspect, in accordance with an environment to which the gas turbine high temperature component is exposed, the thermal barrier characteristic of the thermal barrier coating is varied at the portions of the high temperature component, and thereby, it is possible to make uniform the surface temperature of the metal base material. Thus, the surface temperature of the metal base material is made uniform, so that the cooling medium can be reduced. Therefore, it is possible to improve a performance of the gas turbine high temperature component. Moreover, a temperature gradient of a thickness direction is reduced, and therefore, the lifetime of the gas turbine high temperature component can be made long. In addition, it is possible to reduce a hot spot which is a factor of causing a gas holder such as a combustion gas and a cooling gas, so that a reliability of the gas turbine high temperature component can be improved.
In particular, the gas turbine component such as a movable blade or a stationary blade is a component which is exposed to a high temperature vapor. However, in the present invention, the thermal barrier characteristic of these components is improved, and thereby, a gas turbine high temperature component having a reliability in a high temperature can be obtained.
Furthermore, according to the present invention, the surface temperature difference between the portions of the base material is set within 100xc2x0 C. The surface temperature difference is within the temperature range, thus improving a lifetime of the base material.
Furthermore, the thickness of the thermal barrier ceramic layer is varied, and thereby, it is possible to control a heat resistance of the thermal barrier ceramic layer determining a temperature field.
In this aspect of the present invention, by making larger the thickness of the thermal barrier ceramic layer of the leading edge portion or the trailing edge portion of the movable blade or the stationary blade whose temperature becomes high, it is possible to make uniform the surface temperature of the metal base material.
In the present invention, by making larger the thickness of the thermal barrier ceramic layer of the back side or the belly side of the movable blade or the stationary blade whose temperature becomes high, it is possible to effectively make uniform the surface temperature of the metal base material.
Furthermore., the thickness of the thermal barrier coating layer is defined as described above, and thereby, it is possible to make uniform the surface temperature of the metal base material.
According to the present invention, a pore, that is, a space has a high heat resistance, and for this reason, by varying a porosity of a material constituting the thermal barrier ceramic layer, it is possible to control a heat resistance of the thermal barrier ceramic layer determining a temperature field. In other words, the porosity of the thermal barrier ceramic layer is varied, thus making uniform the surface temperature of the metal base material.
The thicker the thickness of the thermal barrier ceramic layer, or the higher the porosity is made, the higher the heat resistance becomes, and therefore, a thermal barrier performance tends to be improved. In the gas turbine movable blade and in the gas turbine stationary blade, by making larger the heat resistance of the thermal barrier ceramic layer of the leading edge surroundings or the trailing edge surroundings which is exposed to a temperature environment more severe than that of the other portions of the blade, it is possible to make uniform the surface temperature of the metal base material.
Furthermore, in this aspect, in the gas turbine movable blade and stationary blade, by making larger the heat resistance of the thermal barrier ceramic layer on the back side which is exposed to a temperature environment more severe than the belly side, making uniform the surface temperature of the metal base material. The porosity of the thermal barrier coating layer is defined as described above, thus making uniform the surface temperature of the metal base material.
The ZrO2 is used as a main component of the material of the thermal barrier ceramic layer. When the ZrO2 exceeds a temperature of 1200xc2x0 C., it causes a crystal transformation. For this reason, conventionally, an oxide-base ceramic has been used and the oxide-base ceramic has been partially stabilized by adding Y2O3 of about 8% to the ZrO2. In the present invention, a material prepared by adding Y2O3 of about 8% to the ZrO2 is used. In addition to the Y2O3, a material prepared by adding MgO, CaO or CeO2 may be used.
In the present invention, HfO2, ThO2 or BeO having a melting point higher than that of the ZrO2 may be used as a material of the thermal barrier ceramic layer, in place of the main component ZrO2. Additionally, Al2O3 which can reduce cost may be used.
In a further aspect of the present invention, by varying the thickness or porosity of the thermal barrier ceramic layer, it is possible to obtain a high temperature component which can control a heat resistance of the thermal barrier ceramic layer.
In the present invention, by varying the thickness or porosity of the thermal barrier ceramic layer, it is possible to obtain a gas turbine high temperature component which can improve a thermal barrier characteristic.
In the present invention, the thermal barrier ceramic layer is formed on the metal base material by means of a thermal spraying process. According to the thermal spraying process, a raw powder is sprayed onto the metal base material at a high speed, so that a proper pore can be formed in the thermal barrier ceramic layer. Therefore, it is possible to improve a fragility of the thermal barrier ceramic layer.
In the present invention, in a case of forming the thermal barrier ceramic layer by using the thermal spraying process, by varying a supply amount of raw powder, a grain size of the raw powder, a feed rate of a thermal spraying gun, a spraying angle of the thermal spraying gun, a spraying distance and a spray power, it is possible to vary a deposition rate (ceramic layer thickness) of the thermal barrier ceramic layer. Thus, the thickness or porosity of the thermal barrier ceramic layer can be varied. In other words, these conditions are intentionally varied at portions of the thermal barrier ceramic layer, and thereby, it is possible to form a thermal barrier ceramic layer having a thickness and porosity variable at the portions thereof.
In the present invention, the thermal barrier ceramic layer is formed on the surface of the metal base material with the use of a physical vapor deposition process. According to the physical vapor deposition process, the thermal barrier ceramic layer deposited on the surface of the metal base material is formed by a longitudinal crystal growth, and therefore, the metal base material and the thermal barrier ceramic layer are hard to be peeled off from each other.
In the present invention, in the case of forming the thermal barrier ceramic layer by using the thermal spraying process or the physical vapor deposition process, a film coating is formed via a plate having different space ratio, for example, a net having a different mesh arrangement, and thereby, it is possible to vary the deposition rate of the thermal barrier ceramic layer. In other words, the space ratio is intentionally varied depending upon the: portions, and it becomes possible to form a thermal barrier ceramic layer having a thickness and porosity variable depending upon the portions thereof.
In summary, as is evident from the high temperature component, a gas turbine high temperature component and their manufacturing method of the present invention, it is possible to obtain a high temperature component capable of controlling the thermal barrier characteristic of the thermal barrier coating in accordance with an environment to which the high: temperature component is exposed. In particular, the obtained high temperature component is applicable as a gas turbine high temperature component used in a high temperature oxidative and corrosive atmosphere in a gas turbine which is used in a combustion gas atmosphere. Therefore, it is possible to provide a gas turbine high temperature component which is excellent in a heat efficiency, a lifetime and reliability of a gas turbine.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.